1. Field of the Invention
This invention pertains to munitions and more specifically to safe and arming mechanisms utilized in aircraft delivered ordnance.
One of the critical elements in conventional ordnance is the safe and arming mechanism the function of which is to maintain the ordnance in a safe condition until proper inputs are received to initiate the arming sequence. Receipt of proper inputs results in the transformation of the safe and arming mechanism into a configuration in which the main explosive charge can be detonated. One basic concept common in safe and arming technology rests in the interruption of the explosive train by imposition of a movable barrier between explosive train components. This concept is rapidly losing favor to the other, and currently more accepted, basic safe and arming concept involving the misalignment and subsequent alignment of explosive train components. That is, in the safe condition primary initiation explosives located within the safe and arming mechanism are maintained misaligned with the ordnance booster and warhead explosives. Transformation from the safe to the armed condition is accomplished by the controlled alignment of the initially misaligned primary initiation explosives, located within the safe and arming mechanism, with the ordnance booster and warhead explosives.
In aircraft applications the arming process is initiated when a unique set of input signals is received within the ordnance indicating its release from the delivering aircraft. Arming ideally occurs after the ordnance has achieved safe separation from the aircraft which is a function of time/distance. Once arming has occurred detonation of the primary initiation explosives within the safe and arming mechanism will cause booster/warhead detonation. Explosive effects resulting from initiation of the primary explosives, while the mechanism is in the safe condition, will be contained within the mechanism and will not be communicated to the booster/warhead so as to cause their detonation.
2. Description of the Prior Art
As noted, experience has caused barrier movement safe and arming configurations to be relegated to secondary status as compared to the use of misalignment/alignment type configurations. This is due to the fact that barrier movement configurations present additional design difficulties, particularly with respect to the barrier itself, while presenting no particular advantages over the use of misalignment/alignment configurations.
Current art safe and arming mechanisms utilize either mechanical escapements or electronic timers to provide safe separation arming delays. Further, many mechanisms incorporate or rely upon stored energy for component movement or alignment power. The use of mechanical escapements is undesirable, first, because escapement technology and manufacturing capability is disappearing with the advent of digital watch technology, second, mechanical escapement flexibility is poor resulting in relatively poor timing accuracy and, third, mechanical escapements are capable of malfunctioning in a "runaway" mode resulting in premature arming.
While electronic timers are extremely accurate, they are susceptible to the "runaway" failure mode to a degree greater than mechanical escapements. Further, existing safe and arming mechanisms do not incorporate reliable mechanical interlocks in conjunction with the use of electronic timers. This is particularly hazardous in applications where stored energy is relied upon to implement arming and the lack of a satisfactory mechanical interlock can result in unwanted arming due to the inadvertent release of the stored energy and the bypassing of the electronic timer entirely. Current art stored energy devices generally utilize stored mechanical or chemical energy. Such devices are often "single shot" devices, incapable of repeated cycling or testing, which results in unacceptably high failure rates both in the failure to arm or "dud" mode and in the inadvertent or premature arming mode.
Another deficiency in current art safe and arming mechanisms is exposed by their usage in hardened target penetrating ordnance. In this type of application the mechanism is relied upon to survive impact and the high accelerations attendant therewith in an armed and operable condition so that warhead detonation can be delayed until penetration of the target has been achieved. Current safe and arming mechanisms display an unacceptably high dud rate in this type of application exhibiting a tendency to be destroyed on impact, in which case the warhead detonation process fails to be initiated entirely, or to severely deform, in which case warhead detonation fails to occur even if the initiation explosives function properly. The high dud rate is based upon the failure of existing technology to establish a safe and arming mechanism configuration capable of withstanding high impacts in a condition in which warhead detonations can reliably be expected to occur.